The present disclosure relates to a gaseous fuel conversion device, and particularly to a gaseous fuel venturi configured to increase power and reduce unwanted emissions of internal combustion engines.
A venturi is used to mix a gaseous fuel, with air, for combustion in an internal combustion engine. This is done, by placing a restriction in the airflow that creates increased air velocity until the restriction is reduced. As the restriction is reduced, a vacuum (i.e., a low-pressure area) is created that is used to draw fuel into the carburetor.
In gaseous fuel venturi type systems, fuel is commonly drawn into the engine by using a spud tube installed in a gasoline carburetor body, a carburetor adaptor placed between the existing carburetor and the air cleaner or by replacing the gasoline carburetor with a whole gaseous fuel carburetor. The venturi is contained within a carburetor or carburetor adapter body. Typically, the spud tube relies on the venturi profile built into the existing gasoline carburetor. Vacuum, created by the airflow through the venturi, draws on the tube to supply fuel similar to a gasoline carburetor design. Carburetors and carburetor adapters commonly use a removable or changeable venturi so that the same body can accommodate different engines, matching venturi size with engine size and fuel type. Airflow and vacuum are used in a similar manner as with a spud tube, but fuel is typically drawn into the system through slots or holes. Venturis in carburetors and carburetor adaptors can be specifically designed for gaseous fuel.
Conventional removable-changeable venturis are typically shaped like an hourglass, as illustrated in prior art FIG. 1. The fuel is supplied to the venturi, through the orifice or load block, by the fuel regulator. As suction from the venturi reaches the fuel regulator, a diaphragm moves. As the diaphragm moves, it actuates a valve that allows fuel to flow to the venturi, through the orifice or load block. Since the pressure from the fuel in the regulator is offset by the suction of the venturi, there is very little vacuum or zero pressure in the hose between the regulator and the carburetor or adapter. Regulators are often fitted with a primer button. This is used to force fuel into the carburetion system to aid in starting. Regulators may also be fitted with an idle circuit that can also be used to aid in cold starts since they force fuel into the carburetion system as well. When used to aid in starting, the primer button is depressed, pushing on the regulator's diaphragm. The diaphragm connects to the regulator's fuel valve, so as the diaphragm moves, fuel is released and delivered to the venturi.
Common venturi systems include a spud, an adaptor, and a carburetor. A spud tube replaces the existing main jet in a gasoline carburetor. Because the “built-in” venturi is designed to work with gasoline, it does not mix air and gaseous fuels properly throughout the entire engine's operating range. The average gasoline carburetor's venturi is designed to create a little turbulence that “helps” gasoline to atomize. Such turbulence in the airflow is counterproductive in gaseous fuel carburetion systems since the gas is a vapor already. Such disruptions in the airflow cause the spud tube to be a very inefficient system for mixing air and fuel. The inconsistent fuel delivery of the spud tube causes loss of power and varying emission levels throughout the operating curve. Hard startirig and power losses over about 50% are common with spuds when compared with the same engine operating on gasoline. Spuds have been popular because of low cost, but are time consuming to install.
Adapters place a venturi, contained in the adapter body, between the carburetor and the air cleaner. The gasoline carburetor's throttle is still used. While adapters are vastly superior to the spud tube, the venturi shape and sizing can radically alter the performance of the engine and fuel delivery. The main disadvantage, with an adapter, is its usual proximity to the gasoline carburetor's venturi. This second venturi can cause some airflow disruptions resulting in some loss of power.
Among venturi type systems, carburetors offer the best performance since there is no restriction from another venturi and the venturi/carburetor body can be specifically designed for the fuel and engine application. However, the distance between the venturi and throttle location is critical. If the venturi is too close to the throttle, the air/fuel mix does not have time to blend properly before hitting the throttle valve (i.e., butterfly). With replacement carburetors, the distance between venturi and throttle is limited because the gasoline carburetor being replaced usually determines gaseous fuel carburetor length. Yet, it is quite common, on many carburetor designs, for the venturi to be placed further in the throat closer to the throttle since most manufacturers design a standard “carburetor body” that is fitted to each application. This throttle/venturi body is commonly fitted between flange adapters for the inlet and outlet of the carburetor.
Multi cylinder engines present special problems regarding emissions. Engines, with two or more cylinders and a single barrel carburetor, have difficulty in balancing the emissions between cylinders. As emission requirements tighten, it is important that each cylinder have similar emissions numbers. If emissions are not balanced, then one or more cylinders must run too lean to compensate for others that are too rich, so that the lowest overall emissions levels can be achieved. The difference in emission levels between cylinders is the result of a common intake manifold, cam profile, and valve timing. As one cylinder takes in fuel, the other cylinder may still be drawing fuel into its combustion chamber at the same time. This is caused by valve overlap and cam profile. Much of this excess fuel does not completely combust and contributes to higher emissions.
The common solution, to emissions variance between cylinders, is to have an individual barrel/venturi/manifold inlet for each cylinder (e.g., a two-cylinder engine would have a two-barrel carburetor). On a gasoline carburetor, both barrels share a common fuel bowl. This does not contribute to problem of emissions variance since each cylinder's main jet meters out the fuel and the gasoline is only drawn into the cylinder when venturi suction occurs. Common to most new multi-barrel carburetor designs, both throttle lever butterfly valves share a common adjustment, but each barrel can have its own idle circuit mixture. However, when operating on gaseous fuel a common fuel inlet into the carburetor or adapter, for a multi cylinder carburetion system (e.g., a two-barrel carburetor) is just about the same as having a single barrel carburetor since both cylinders draw from a single source. The fuel regulator can also contribute to variances in cylinder emissions. Most modern two cylinder engines, for example, have an “intake, intake, exhaust, exhaust” not “intake, exhaust, intake, exhaust” stroke pattern. While the first cylinder takes in fuel, the gaseous fuel regulator's diaphragm/fuel valve has not yet retracted before the second cylinder takes in fuel. The fuel valve remains partially open. The result is an extra rich intake stroke for the second cylinder. Even at idle this is a concern since the regulator's internal idle circuit delivers pressurized fuel at low speeds with the same result. Existing gaseous fuel carburetor designs (venturi and non-venturi types), both single barrel and multi-barrel, may have an idle circuit by-pass that supplies fuel between the fuel inlet port and the load-block or metering valve. In such designs, all cylinders share the same air fuel mixture for idle, so the single adjustment does not address idle circuit related emissions variance. Also common to existing multi-cylinder carburetion designs is a common fuel inlet port to the carburetor, or carburetor adapter, that supplies fuel to all cylinders. Because of these challenges, each cylinder needs its own metered fuel mixture.
There are several challenges not addressed by current venturi style conversion systems. These challenges include current spud tube, adapter, carburetor and venturi designs, which rob too much power from the engine because of inefficient airflow designs. These inefficiencies also produce inconsistencies in fuel delivery that prevent a catalytic muffler (if present) from performing properly. Current carburetion designs may pass current certification requirements (i.e., high speed, full throttle) but may not pass future certification requirements that consider varying loads and speeds. This will be especially true when the emission levels require a catalytic muffler to meet the standards. Current carburetor and adapter designs still use a common inlet for multi-barrel carburetors and adapters. This prevents each cylinder from receiving a precise amount of fuel needed to minimize emission levels.
What is needed in the art is a gaseous fuel venturi configured to increase power and reduce unwanted emissions of internal combustion engines.